1. Field of the Invention
The invention relates, in general, to laser guided weapon systems and, more particularly, to boresighting a 1.06 micrometer designator laser to any or all of the three sighting systems used in the Target Acquisition Designation System (TADS) and proposed by Northrop Corp. for the YAH-64 aircraft.
2. Description of Prior Art
One of the major potential sources of error in laser guided weapon delivery is boresight misalignment between the laser designating a target and the sighting system being used to aim at the target. The TADS has visual direct view, day TV, and Forward Looking Infrared (FLIR) sights which must be aligned with respect to the laser. Thus, a single boresighting method and apparatus usable by all of these sighting systems would be desirable. Since the boresighting techniques must conform to the specific requirements of the system, examples of techniques used with other aircraft laser designator sighting systems are discussed to highlight the specific requirements of TADS. Some of the examples will also be shown schematically in drawings that follow, since they help understand the evolution of the present system. These sighting systems were expanded and improved upon in the development of the present boresighting method for the TADS.
The Stabilized Platform Airborne Laser (SPAL) built for the U.S. Army consists of a laser designator/ranger, a high resolution adaptive gate TV autotracker camera, and target acquisition laser spot tracker, all of which are mounted in a two-axis stabilized platform. SPAL is boresighted by retroreflecting the attenuated laser beam into the 1.06 micrometer sensitive silicon vidicon TV camera, then manually centering the electronic aim-reticle and video autotracker electronic null on the laser spot. Airborne on a UH-1 helicopter, SPAL designated tank targets at long range during the first successful Hellfire (laser spot seeker) missile firing tests in 1974 (See FIG. 1).
The AN/AVO-27 Laser Target Designator Set (LTDS) is a small, rear-cockpit-mounted unit designed to provide laser designation, surveillance, reconnaissance, forward air observer, and bomb damage recording capability for two-seat aircraft, such as the Northrup F-5B and F-5F. It consists of a 16 mm camera, a direct view telescope (4X and 10X), and high-power laser which is projected by a lens common to the visual telescope. The laser beam is aimed by the operator's thumbforce controller imputs to a gyrostabilized mirror. During laboratory testing, it was first proven that the aim-reticle of the visual telescope sight could be aligned on a visual flash generated by the laser beam, while the latter was being focused on a target in a test collimator. (See FIG. 2).
The Laser Augmented Target Acquisition/Recognition (LATAR) system includes a high resolution 4:1 optically-compensated zoom lens, an adaptive-gate TV autotracker camera, and a laser designator/ranger (or operator-selectable laser-spot tracker). All are mounted within a self-contained pod and coupled through a two-way optical joint to a common objective lens. The lens is mounted in a gyro stabilized head having a 300-degree spherical field-of-regard. LATAR has been successfully flight tested on F-5E and F-4E aircraft. The system was boresighted by illuminating a pinhole (drilled by the LATAR laser) in a target at the focal point of an auxiliary collimator telescope.
The Light Observation Helicopter Target Acquisition/Designation System (LOHTADS) has a FLIR video sensor and separate aperture laser designator rangefinder. It is aimed manually or automatically by an adaptive-gate video target tracker. Boresighting the FLIR sensor of LOHTADS while airborne was proposed to be accomplished by aligning on collimated radiation emitted from a "hot flash", the "hot flash" being generated by the laser at the focal point of a reflective telescope. (See FIG. 3).